code: def __contains__(self, key):
      return dict.__contains__(self, key.lower())
  
file_path: nltk/nltk/sem/lfg.py
imports: from itertools import chain
  from nltk.internals import Counter
label_desc: Use image node_id 4 for calling the FStructure obj's underlying member method code with example usage: obj.__contains__(key) and returns: dict